During the twentieth century, tire designers and manufacturers have conceived of various designs with which to enable a pneumatic tubeless tire to continue to function even after a loss of air pressure. Generally, a tubeless tire is made of a tread section with two sidewalls. Beads are located at the end of each sidewall and are typically rigid. The beads fit onto a rim. Putting air pressure into the interior of the tire causes the beads to seat against the rim and securely hold the tire onto the rim.
The design and use of a run-flat tire is desirable for several reasons. First, sudden loss of air pressure in a tire can result in a shifting of the position of the tire, and subsequently a change in the internal tensioning forces originally imparted by the tire on the rim to hold the tire thereon. The tire may become disengaged from the rim under certain circumstances.
Second, a loss of air pressure forces the tread of the tire onto the rim. The rim must then assume the loading from the weight of the vehicle and the dynamic forces of the ride. As the rim is not designed for this purpose, damage to either the rim, wheel, axle, or suspension can result. This in turn can lead to costly repairs in addition to leaving the driver and passenger stranded once the rim is too severely damaged to continue riding.
One such design of a run-flat tire is disclosed in U.S. Pat. No. 5,427,166 to Willard, Jr., which is owned by the assignee of the present invention and is incorporated by reference herein in its entirety for all purposes. This tire has thickened sidewalls which are designed to bear the load of the vehicle in the event of loss of tire inflation pressure.
Another run-flat type tire is the vertically anchored tire disclosed in U.S. Pat. No. 5,891,279 which uses a flexible insert mounted on the wheel rim to support the vehicle load if the tire loses inflation pressure.
Run-flat tires are desirable over conventional tires because with reasonable and appropriate action by the driver, such tires can allow limited, continued mobility for travel to a location where the tire can be inspected, repaired, or replaced as necessary.
It is sometimes the case that run-flat tires, and also conventional tubeless tires, are driven in a condition where they are subjected to lower than normal operating pressure. In such instances, pressure loss will only be severe enough to cause the sidewall of the tire to flex. Flexing in these circumstances will impart stress on the sidewall of the tire and possibly other areas as well. Although designed to accommodate some degree of flexing, sustained flexing or severe flexing of a tire may lead to the tire being damaged and unsuitable for further use.
Therefore, it is desirable to have an indication whether a tire has been too severely damaged after experiencing a condition of lower than normal operating pressure. If the tire has been subjected to an acceptable amount of stress, a technician or motorist may repair the tire for continued use. If the tire was too severely damaged, the technician or motorist may discard the damaged tire and install a new one.
Typically, if a conventional tire has been subjected to a condition of low tire pressure, “wrinkles” will develop on the inside and/or outside of the sidewalls of the tire. The wrinkles are cracks and/or marks due to stress brought about from an unacceptable degree of flexing of the tire. Run-flat tires may also exhibit wrinkles if operated in a condition or undesirable low tire pressure. Tires are typically deemed unfit for further use once the presence of wrinkles is noticed. However, the tire may still be unsafe and/or unfit for further use even when wrinkles are not present. Additionally, wrinkles may sometimes be hard to spot or subject to subjective interpretation by a technician or motorist.
The present invention provides for a low or no pressure use indicator that is located on a tire, either a conventional tire or a run-flat tire, in order to inform a technician or motorist whether the tire has been subjected to an undesirable condition of low pressure.